Secretary of State Rex Tillerson said the US govenment had "no doubt" Syrian regime leader Bashar al Assad was behind the suspected chemical attack killed scores of civilians on Tuesday.

US Secretary of State Rex Tillerson.

Washington would make an "appropriate response" to Tuesday's suspected chemical attack in Syria, the US Secretary of State Rex Tillerson on Thursday.

Tillerson said the US government had no doubt that Bashar al Assad was responsible for a chemical weapons attack that killed scores of civilians in the town of Khan Shaykhun on Tuesday.

"We are considering an appropriate response (to the) violations of all previous UN resolutions, violations of international norms," he said in Florida, where he greeted Chinese President Xi Jinping who was arriving for a summit with US President Donald Trump.

Tillerson did not specify what actions the United States would take.

Assad's role in the future is uncertain and with the acts that he has taken, it would seem that there would be no role for him to govern the Syrian people.

TRT World'sAzadeh Ansari has more details from Washington, DC.

Military action against Assad

The Pentagon and the White House are in detailed discussions on military options to respond to the gas attack, a US official said on Thursday.

The options could include grounding aircraft used by Assad's forces, the official added, speaking on condition of anonymity.

Such options would also include use of cruise missiles — allowing the United States to strike targets without putting piloted aircraft in the skies above Syria.

The official did not comment on how likely military action might be or suggest which, if any, options might be recommended by the Pentagon.

But the official added that US Defense Secretary Jim Mattis and White House national security adviser H.R. McMaster had already been in talks on the matter.